I recently bought a 2004 f 42 Lightning two 525 Efi in Italy
I have installed Stelling extension boxes and -2 imco lowers ending with the propshaft 1" below
I did the first test on the lake of Como few days ago with 32p Max 5 labbed and full tanks and three people
Result is
I need tho go very carefully for planing (long way) tabs down drives in and keep us some speed than up some tabs a away it goes (easy to blow out props if over 3000 rpm)
Fists trial max speed (Gps) 80.5 mph at 5000 rpm.
have any of you any thoughts about the setup/propeller and results? it seems very high propeller slip more than 20%??

sorry 2004 Fountain 42 lightning full staggered 525s bravo XRs

Speed is OK or close to it with 525's in 42?

What is the elevation on Lake Como? Most 42 stag fountains of that year did NOT use extensions boxes.

One without boxes and light (Low on gas, 1 person etc) did 87 in the shootout. I believe most would run an everyday speed in the 82 range so you are close. Do you have a head, gen set or AC?

Always want to go to that lake since the 80's when DUCATI would do photo shoots there.

elevation of the lake is 200 meters, 650 feet

no air conditioner no generator

I have been trying stock Maximus 30 Pitch same speed (80) at 5300 rpm
much better planing on shorter distance.
next trial stock Bravo 4 blade 32 p

I don't have extension boxes, I'm running standard Bravos with Bravo 32P 4 blades and mine comes up like a dream. It takes a few minutes and some patience but I don't "bury" the tabs or drives when coming up on plane. Tabs at 2-3 and drives around 2-2.5, bring up the RPMs and allow the boat to blow out slightly while feathering to not over rev. I allow some time at this point to gain momentum... Keep it below 3200-3500 while getting moving. Start bringing tabs up uninterrupted to positive trim. Loosen it up with the drives and enjoy the ride! Don't trim past out past 5!
These things are heavy and need momentum with mild power.....
*2005 42 EX with staggered 525s

I'm open to correction if anyone has any....

have you of your propshaft height or X dimension to compare with mine?

Your X dimension would be -2" from mine or your shaft/props are more than likely a couple of inches higher than mine but that would not impact 'how' you will come up on plane. Your blow out will be more pronounced and it will take a bit longer for them to bite. The time taken to gain enough momentum for the bite will be extended slightly but the order of events and the actions to achieve it would not differ....
Hope this helps!